Existing mass spectrometers have an ion source that produces ions of a sample material. These ions are then processed by a mass analyzer which includes a mass detector. Some existing ion sources produce ions using a technique known as electron ionization (EI) and others using a technique known as chemical ionization (CI). In both EI and CI, an electron source is configured to selectively provide a stream of electrons to the ion volume. The electron source includes a filament that is energized to emit electrons for the stream. It is advantageous to provide a second filament. When one of the filaments burns out, an operator can continue running samples with the other filament. As such, the mass spectrometer is not rendered completely inoperative by a burned-out filament, and can continue operating with minimum disruption.
However, no two filaments are exactly the same. For example, each filament may produce a different ion intensity while the mass spectrometer is operating under the same operating conditions. The ion intensity can be as different as a factor of two. Differences can be caused by small variations in filament position, reflector position, filament alignment with the ion volume, filament composition, or other factors. Accordingly, the mass spectrometer is normally recalibrated when switching filaments to ensure that the mass spectrometer continues to generate accurate and consistent data when running samples with the other filament. However, recalibration is time consuming, and requires scrapping the sample run that was currently in progress before the burnout.